1Field of the Invention
The present invention relates to systems and methods for sealing leaks. More particularly, the invention relates to a system and method for sealing leaks in vessels containing hazardous coolants, insulants, and other potentially harmful compounds.
High voltage electrical equipment, such as large circuit breakers and transformers, include conductors that are typically encased in an insulator, also known as a bushing assembly, which comprises one or more sections of cylindrical porcelain pipe that surround the high voltage conductors. The sections of pipe define respective joints at the pipe interfaces which are sealed with compression seal o-rings and the like. The insulators are often filled with inert, non-conductive gasses and/or oils for cooling and insulating purposes. One such gas is sulfur hexafluoride (SF.sub.6).
While SF.sub.6 is quite effective as an insulant, the gas also suffers from at least one significant shortcoming. It has been found that SF.sub.6, if it escapes from its containment and is released into the atmosphere, depletes the ozone layer. Therefore, the gas has been targeted by the Environmental Protection Agency (EPA), and strict regulations have been imposed on its use, both in the United States and throughout the world. Moreover, SF.sub.6 has recently become very expensive. Therefore, a leak is not only an environmental concern, but can also be very costly.
Some high voltage electrical equipment, in particular transformers and some circuit breakers, utilize "transformer oil", which is a mineral oil that is an effective insulant and coolant for the electrical equipment. However, transformer oil also has drawbacks, one being that it degrades gaskets, o-rings, and seals, often causing them to leak. Transformer oil, if allowed to leak for continued periods of time, is potentially damaging to the environment as well.
Others have attempted to solve the above-described leaks with various methods and devices. One proposed method was to simply ignore the leak until the electrical equipment could be taken off line, removed from the site, transported to a repair facility, and repaired by disassembling the bushing and replacing the leaking seal. Typically, the amount of time that elapsed before such action was taken was on the order of decades. Not only is this method very burdensome and expensive, but with increasing environmental concerns and strict regulations, this method is no longer feasible, as an SF.sub.6 leak may no longer be ignored for such an extended period of time.
Yet another method practiced by others in the past was to depressurize the electrical equipment, apply a layer of silicone caulk or the like onto the outside of the leaking joint, repressurize the electrical equipment, and put it back into service. This method rarely, if ever, works because often the surface of the equipment cannot be properly prepared in the field, and thus the caulk does not bond sufficiently well to the insulator surface. In addition, the caulk often does not have sufficient inherent strength or bonding strength to withstand the stresses resulting from the pressurized gas trying to escape, and therefore the caulk fails after a relatively short operating life. Furthermore, such a method suffers from the shortcoming that the electrical equipment must be fully depressurized for a period of time while the caulk is applied and allowed to cure.
Still another proposed method is to apply a layer of caulk or the like to the joint, and then apply a reinforcing layer over the caulk. However, the caulk still tends to fail as a result of differences in the coefficient of thermal expansion between the caulk and the leaking surface, such that during the first thermal swing (usually the same day), the caulk either cracks or debonds, thereby destroying the seal.
Yet another method involves the fabrication of a close-fitting housing that encloses the leaking joint. The housing is constructed with a passageway extending fully around the leaking joint, directly over the joint and opening toward it. Thus, once the housing is in place over the leaking joint, a pump is connected to the housing and sealant is pumped into the passageway. The sealant is pressurized to a level higher than the pressure of the leaking fluid. The wall of the leaking components and the walls of the housing serve to hold the sealant in place until it cures.
While this method has proven somewhat effective at sealing the leak, it has a number of shortcomings. In the first place, the sealant actually adheres the opposite sides of the leaking joint together, which makes it more difficult to take the joint apart at some later date in order to perform a permanent repair of the leaking joint. In addition, leaking joints typically have different configurations and different dimensions. Even similar joints on the same equipment often have significant dimensional differences. Thus, each joint requires a specially configured housing, which is obviously burdensome, inefficient, and expensive. Furthermore, because the sealant is pressurized to a level higher than that of the leaking fluid, the sealant may actually be forced into the electrical component through the leak itself, which can result in a dangerous equipment failure.
In addition, the assignee of the rights in the present invention proposed a method and system marketed under the name "Power Band 1". The method involved wrapping plural turns of tape about the leaking joint, with a number of small tubes extending from beneath the tape to the atmosphere to allow SF.sub.6 gas passing through the leaking joint to escape from under the tape so that the tape properly lays down over the joint. A composite layer is placed over the tape, and the small tubes are crimped. While this method has enjoyed success, it has been found that the small tubes often leak. In addition, the method requires precision in laying down the tape.
Accordingly, it will be apparent to those skilled in the art that there continues to be a need for a system and method that effectively stops leaks without the need for depressurizing the equipment. Furthermore, there exists a need for such a system and method that can be readily adapted in the field to stop a leak in any joint, regardless of the dimensions of that joint. The present invention addresses these needs and others.